GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER-V (NEW) EXAMINATION - WINTER 2020
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Subject Code:2150908 Date:20/01/2021Subject Name:Electrical Power System — I
Time:10:30 AM TO 12:30 PM Total Marks: 56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
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2. Make suitable assumptions wherever necessary.3. Figures to the right indicate full marks.
MARKS
Q.1 (a) Discuss the advantage of high transmission voltage 03
(b) State and prove the Kelvin‘s law for size of conductor for 04
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transmission.(c) A 50Km long transmission line supplies load of 5 MVA at 0.8 07
p.f lag at 33 KV. The efficiency of the transmission line is 90
%. Calculate the volume of conductor Aluminum required for
the single phase 2 wire system. Take resistivity of Aluminum
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as 2.85 x10 -8 O.m Q.2 (a) What is skin effect why it is absent in d.c 03
(b) What is the effect of unsymmetrical spacing of conductor in 04
three phase transmission system?
(c) Drive the expression for the capacitance of single phase 07
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transmission line. Q.3 (a) Define and explain string efficiency- Can its value be equal to 03
100?
(b) Give reasons for the following : 04
(1) A.C.S.R. conductors are preferred for transmission and
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distribution lines.(ii) Conductors are not fully stretched between supports
(c) An insulator string consist of three units, each having a safe 07
working voltage of 15kv. The ratio of self-capacitance to shunt
capacitance of each unit is 8:1. Find the maximum safe
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working voltage of the string. Also find string efficiency. Q.4 (a) List out line supports with its three features 03
(b) What are the factors that affect the sag in the transmission line? 04
(c) Discuss the various conductor material used for overhead line. 07
What are their relative advantages and disadvantages?
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Q.5 (a) What is the main difference between AC and DC distribution 03
system
(b) Drive the expression for capacitance of single core cable. 04
(c) Discuss the advantages and disadvantages of (i) pin type 07
insulator (ii) suspension type insulator
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Q.6 (a) With neat diagram, show the various part of high voltage 03
single core cable
(b) What are the different types of distribution system? 04
(c) What are the different types of substation layout used in distribution system? 07
Q.7 (a) What are the advantages of per unit system 03
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(b) How the current distribution and the voltage at various loading 04points can be determined in a DC ring type distribution
system?
(c) A DC two wire distributor 250 m long and fed at one end is 07
load uniformly at the rate of 1.6A/meter. Total resistance of
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the distributor is 0.0002 ohms/meter. Determine the voltage atthe fed to maintain at 250 V. (i) at far end (ii) at the midpoint
of distributer.
Q.8 (a) Define and explain primary and secondary distribution system 03
with single line diagram
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(b) Represent p.u model of transformer with and without tap 04changer.
(c) Derive expression for inductance per phase for 3-ph overhead 07
transmission line when conductors are asymmetrically place
but transposed
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